There are multiple convergent lines of evidence suggesting that apoE (apolipoprotein-E) plays an important role in modifying clinical outcome in acute and chronic neurological diseases. These clinical observations, based on apoE genotype of the patient, are consistent with murine models of stroke and traumatic brain injury (TBI) in which apoE exerts neuroprotective effects (Laskowitz et al. 1997, Sheng et al. 1998, 1999, Lynch et al., see below).
ApoE is a 299 amino acid protein with multiple biological properties. First identified for its role in the transport and metabolism of cholesterol and triglycerides, apoE serves as a ligand for the low density lipoprotein (LDL) receptor, the LDL-receptor related protein (LRP) and the very low density lipoprotein (VLDL) receptor (Weisgraber 1994). In addition to its role in cholesterol metabolism, recent compelling clinical data suggests that apoE also plays a significant role in the neurobiology of acute and chronic human disease. There are three common human isoforms, designated apoE2, apoE3, and apoE4 which differ by single amino acid interchanges at residues 112 and 158 (Weisgraber 1994). Presence of the APOE4 allele has been associated with increased susceptibility of developing late onset familial and sporadic Alzheimer's disease (AD). Recent clinical evidence also strongly implicates the presence of the APOE4 allele with poor outcome following acute brain injury (See, Laskowitz et al. 1998a, 1998b, Crawford et al. 2002).
It has been observed that apoE influences development of late onset and familial AD. This effect is robust and dose-dependent, such that homozygous individuals with an APOE4/4 genotype have an approximately 20-fold increased risk of developing AD, and heterozygous individuals with an APOE3/4 genotype have a 4-fold increased risk relative to patients who are homozygous for the most common APOE3/3 genotype (Strittmatter et al., 1993; Corder et al., 1993; reviewed by Laskowitz et al., 1998a). This observation has led to a resurgence of interest in the function of apoE in the mammalian central nervous system (CNS). Because of its association with AD, multiple laboratories have examined interactions between apoE and proteins believed to play a role specific to the pathogenesis of AD. Thus, several laboratories have described isoform-specific interactions between apoE and Abeta or apoE and tau (Strittmatter et al. 1994; Gallo et al. 1994; Fleming et al. 1996; reviewed by Laskowitz et al., 1998a). The role of apoE in the CNS, however, remains undefined and it is unclear which of these interactions are relevant in human neurodegenerative disease.
Traumatic brain injury (TBI) is a leading cause of injury-related death and disability among children, young adults and the elderly in the United States. Epidemiological data have demonstrated the serious socioeconomic impact of TBI to society estimating that the cost of hospital care alone exceeds $1 billion per year. The estimated incidence of TBI doubles between the ages of 5 and 14 years, and peaks for both males and females during early adulthood to approximately 250 per 100,000. Because the lives of most survivors of moderate to severe TBI involve chronic, life-long neurological disabilities with varying degrees of dependence, the cost in individual suffering, family burden, and financial burden to society may be greater for those who have more years to live. Thus, there is a need for improved treatments for TBI.
U.S. application Ser. No. 10/252,120, filed Sep. 23, 2002, discloses methods of using apoE analogs, including COG133, to treat or ameliorate the neurological effects of cerebral ischemia or cerebral inflammation. COG133 is a small truncated peptide, comprised of residues 133-149 of the entire apoE protein. While COG133 has proved useful in animal studies, it has a limited treatment window within which it must be administered. Thus, there is still a need for improved treatments for TBI.
In addition to TBI, toxicities associated with chemotherapy and radiotherapy can adversely affect short and long-term patient quality of life, can limit the dose and duration of treatment, can be life-threatening, and may contribute to both the medical and non-medical care costs. Adverse consequences of cancer treatment have led to the development of specific agents designed to ameliorate or eliminate certain chemotherapy- and radiotherapy toxicities. The ideal chemotherapy- and radiotherapy-protectant agent would prevent all toxicities, from non-life-threatening side effects (alopecia) to irreversible morbidities (hearing loss, neurotoxicity) to potentially fatal events (severe cardiomyopathy, severe thrombocytopenia), without adversely affecting the antitumor efficacy of the cancer therapy, and would be easy to administer and relatively nontoxic in its own right. However, most agents developed to date have a much narrower spectrum of toxicity protection (Hensley et al., 1999).
Xerostomia and mucositis are major toxicities that are associated with radiation therapy. The risk of these complications is related to the area undergoing radiation, the dose and schedule of radiation therapy, whether radiation therapy is combined with chemotherapy, and a number of host-disease-related factors that are only partially understood (Mossman, 1994). Although these toxicities are rarely associated with mortality, the morbidity can be quite significant for patients, with acute and long-term consequences. Xerostomia is the most common toxicity associated with standard fractionated radiation therapy to the head and neck region. Whereas acute xerostomia from radiation is due to an inflammatory reaction, late xerostomia, which includes xerostomia occurring 1 year after radiation, reflects fibrosis of the salivary gland and, as such, is usually permanent. Xerostomia results in symptoms of dry mouth; this affects the patient's ability to eat and speak. Additionally, patients with xerostomia are at an increased risk for dental caries, oral infections, and osteonecrosis.
Radiotherapy is the primary treatment for patients with brain cancers. Independent of the modality with which the radiation is delivered to the brain (medical therapy, attacks or nuclear accidents), the brain typically responds in a slow manner with severe clinical symptoms indicating brain cell death (Fike et al., 1988). While these problems are severe and may be fatal over a course of months, less severe acute symptoms are also debilitating in the days to weeks following radiotherapy (Mandell et al., 1990).
The reasons for the death and/or dysfunction of brain cells are not precisely known, but are thought to arise from a variety of responses following the application of radiation. Ionizing radiation causes damage to living tissues through a series of molecular events depending on the radiation energy. Acute radiation damage is due to the aqueous free radicals, generated by the action of radiation on water. The major free radicals resulting from aqueous radiolysis are OH., H., HO2, H3O+, etc. (Scholes, 1983; Pradhan et al., 1973; Dragaric and Dragaric, 1971). These free radicals react with cellular macromolecules, such as DNA, RNA, proteins, and membranes and cause cell dysfunction that may ultimately lead to mortality. The radiation damage to a cell is potentiated or mitigated depending on several factors, such as the presence of oxygen, sulfhydryl compounds and other molecules in the cellular milieu (Pradhan et al., 1973; Bacq 1965). In the presence of oxygen, hydrated electrons and H atoms react with molecular oxygen to produce radicals, such as HO2, O2−, apart from other aqueous free radicals (Baraboi et al., 1994; Biakov and Stepanov, 1997).
Beyond the direct effects of radiation to generate radical species, several reports document the release of cytokines in the brain following radiation treatment (e.g., Girinsky et al., 1994; Hong et al., 1995; Chiang et al., 1997). In particular, Hong et al. (1995) report that mRNA for tumor necrosis factor alpha (TNFa), interleukin 1 alpha and beta (IL1a and IL1b) significantly increased in the brains of mice receiving a single 25 Gray (Gy) dose of brain irradiation, a dose that translates to less that 10% mortality. To a lesser extent, interleukin 6 (IL6) is also induced in a dose dependent fashion with increasing radiation dose. Total body irradiation generated a similar pattern of cytokine induction, but the levels of induction were much less than those seen with brain-specific irradiation. These observed changes in cytokine levels following irradiation are consistent with the astrocytosis and microgliosis associated with the typical innate immune response that the brain mounts in response to disease and/or invasion of pathogens. As reported in our recent publication (Lynch et al. 2003), peripheral treatment with lipopolysaccharide (LPS) can also induce a brain inflammatory response which includes astrocytosis, microgliosis and cytokine release similar to that seen by these authors with radiation treatments.
Three agents are currently approved by the United States Food and Drug Administration (FDA) for chemotherapy and/or radiotherapy protection: dexrazoxane, mesna, and amifostine. However, each of these approved agents has significant issues that limit their efficacy. Dexrazoxane and mesna each have relatively limited spectra of toxicity protection, cardiac and urothelial, respectively, whereas amifostine has a broader potential cytoprotection spectrum. The good news is that these agents (with the probable exception of mesna) act systemically, are not clearly targeted to one specific cell type, and probably function to protect most cell types. Unlike myelosuppression or acute nausea/vomiting, measurement of the toxicities associated with these agents are more difficult or labor-intensive to reproducibly assess in clinical trials because of outcome subjectivity (neurotoxicity), latent onset (cardiomyopathy), or unclear clinical relevance (asymptomatic increases in serum creatinine, microscopic hematuria, or asymptomatic decreases in cardiac ejection fraction) (Hensley et al., 1999).
Amifostine, formerly known as WR-2721 and whose active metabolite is an aminothiol, can protect cells from damage by scavenging oxygen-derived free radicals. This drug arose from a classified nuclear warfare project sponsored by the United States Army and was ultimately selected from a group of more than 4,400 chemicals screened because of its superior radioprotective properties and safety profile (Schucter and Glick, 1993). Subsequently, amifostine was evaluated for its potential role in reducing the toxicity of radiation therapy and of chemotherapeutic agents that alter the structure and function of DNA, such as alkylating agents and platinum agents. Unlike dexrazoxane and mesna, for which the protective effects are directed against specific organs, amifostine has been evaluated as a broad-spectrum cytoprotective agent. A profile emerged from preclinical studies that demonstrated the ability of amifostine to selectively protect almost all normal tissues, except the central nervous system (CNS) and neoplastic tissues, from the cytotoxic effects of radiation therapy (Schucter and Glick, 1993; Coleman et al., 1988). Accordingly, there remains a significant need for effective treatments to reduce the effects of radiation and radiotherapy, particularly in the brain and CNS.
Inflammatory bowel disease (IBD), also known as Crohn's Disease or ulcerative colitis, affects approximately 1 million Americans with inflammation of the intestines, abdominal pain, cramping, and diarrhea. These symptoms vary in severity, but are often debilitating for patients to the extent that they greatly alter their quality of life. There are a wide array of therapies available, with nearly all patients requiring a combination of treatment modalities depending on the severity of disease. These treatments, however, are often very expensive as is the case with infliximab (anti-TNF monoclonal antibody), and typically display major unwanted side-effects such as seen with corticosteroids and immunosuppressants that include risk of infections or malignancies, diabetes, pancreatitis, and severe bone loss. In addition to these problems, the extensive morbidity faced by IBD patients is a clear driving factor for continued efforts to develop new and effective therapies. Although apoE appears to have beneficial effects in innate immunity, as evidenced by loss of innate immunity to systemic infection and exacerbation of sepsis and inflammation in apoE-deficient mice, the role of apoE in intestinal inflammation remains completely unexplored.